A. Field of the Invention
The present invention is related to brake beams for railway cars, and more particularly to an improved unit guide wear plate for brake beams, which aligns the movement of a brake beam end guide within the side frame of a railroad car truck so that the brake shoes are lined up to provide the maximum amount of force against the wheels when stopping the railroad car. Additionally, the unit guide wear plate of the present invention improves the lateral alignment of the brake shoes on the wheels.
B. Background of the Invention
There are well known brake heads assemblies for railway cars by which a brake shoe is pressed against a wheel in order to decrease or stop the rotational speed of the wheel and of the railway car.
Generally, two brake head assemblies are held by a structure called a “brake beam” mounted transversely in the truck of a railway car and are pinned to levers, which apply forces in order to press the brake shoes against the wheels.
The brake beam generally comprises, a tension member having two opposed ends; a compression member also having two opposed ends respectively coupled to the ends of the tension member; a brake head subassembly linked to each end of the compression member, two end extensions each coupled to an end of the compression member by which the brake beam is supported in the truck of a railway car; and a fulcrum coupled to the compression and tension members, so that the fulcrum remains between the tension member and the compression member. The end extensions of the brake beam are confined within respective pocket guides of the truck.
The lateral angle between a brake beam and a lever of the rigging system causes the brake beams to shift sideways when the braking force is applied, and to impinge on the side frames of the truck at diagonally opposed locations.
Current available brake shoes, are hardened in order to extend their lifetime, and designed to smooth any surface defect on the truck wheels (known as tread conditioning shoes). Although the cost of a new design brake shoe is approximately six times higher than the cost of a conventional brake shoe, it is in high demand since replacing the wheels is the costliest and most important maintenance element in a railway car.
New truck designs are made more flexible, in an effort to reduce the wear of the wheel treads, but because of such flexibility, the lateral movement of brake beams is greater.
When a brake beam moves laterally, one of the brake shoes can make contact with the flange of one wheel on the corresponding axle (overriding condition). This together with the new brake shoe design, and the flexibility of the new truck designs, can cause excessive wear of the flange and a premature replacement o the wheel. Meanwhile, the other brake shoe, extends beyond the opposite wheel tread (overhanging condition). As this brake shoe wears out, it begins to wear and heat the lateral face of the corresponding wheel thus creating micro cracks, which can be confused with profound cracks upon inspection, thus condemning the wheel.
In view of the above referred problems, there have been developed devices for centering the brake beam and avoiding its lateral displacement, such as the U.S. Pat. No. 5,421,437 which discloses a unit guide wear plate which aligns the movement of a brake beam end guide within the side frame of a railroad car truck so that the brake shoes can provide the maximum amount of force against the wheels when stopping the railroad car. The unit guide wear plate is comprised of a wear plate body, having a u-shaped cross section, a first side wall, having a first inner surface and a first outer surface; a second side wall, having a second inner surface and a second outer surface; a third side wall having a third inner surface and a third outer surface; wherein the first side wall is located such that it is attached to the third side wall opposite the second side wall; a first flange extension protruding from the first side wall and a second flange extension protruding from the second side wall; a pair of dimples arising out of the second outer surface for securing the unit guide wear plate within a railroad car side frame; a spring tang for providing a lateral force on a brake beam end guide as it lies within the unit guide wear plate body; and a first ramp extending outward from the first inner surface and a second ramp extending outward from the second inner surface, for aligning the brake beam end guide within the unit guide wear plate body. U.S. Pat. No. 5,421,437 discloses many embodiments of the unit guide wear plate, including the substitution of the spring tang with a metallic insert as shown in FIG. 5 of U.S. Pat. No. 5,421,437.
However, the unit guide wear plate disclosed in U.S. Pat. No. 5,421,437 has several problems since it tends to fracture while in service and is not strong enough to really align the brake beam.
In view of the above referred problems applicant developed an improved unit guide wear plate in which the spring tang is wider and flatter, thus providing a wider surface for pushing the ends of any kind of end extension.
The improved unit guide wear plate of the present invention has an insert preferably made of an elastomeric material that works together with the spring tang, providing additional resisting force and lowers stresses in the spring tang. This new feature avoids the observed fracture of the unit guide wear plate, tang while developing a higher brake beam centering force.